The present invention relates to damping, more particularly to methods, apparatuses and systems for passively effectuating damping for controlling vibrations.
Vibrations are often unwanted because they can cause structural weakening, metal fatigue, bothersome noise, etc. Particularly undesirable are many situations wherein a power-driven source (e.g., a motor) produces a frequency at which an attached structure naturally vibrates, an occurrence known as "resonance."
Various types of passive damping treatments have been known to be effective in reducing the amplitude of vibrations at resonant frequencies. The known effective passive damping methodologies include "conventional" damping, "entrained" damping and "tuned" damping.
Two known kinds of conventional damping treatment are unconstrained (unconstrained-layer) damping treatment and constrained-layer damping treatment. All of these known passive damping mechanisms, though often highly (or at least moderately) effective for particular applications, nonetheless have limited capabilities in terms of damping performance.
Tuned damping, for example, produces a relatively large loss factor in a narrow frequency band. Therefore, tuned damping is generally applied to reduce single mode vibration. In contrast, constrained-layer damping is effective in a broad frequency, but its loss factor is relatively small. Because of this, constrained-layer damping treatment is relatively effective for controlling the vibrations in higher frequencies, but is less effective in lower frequencies.
A greater amount of damping loss factor has been known to be achieved by applying an increased number of similar passive damping treatments on the structure; however, this sort of "pluralizing" approach to individual units yields a diminishing return in damping effectiveness as the amount of damping treatment (i.e., the number of units) increases.
Active (as distinguished from passive) vibration control methodologies have also been known to effectively reduce vibrations. However, due to limitations regarding processor speed and actuator power delivery, active vibration control has proven rather impractical in high frequency and multi-mode vibration control. Moreover, the costs associated with installation and maintenance of active vibration control systems, vis-a-vis' passive vibration control systems, are comparatively high.
Generally speaking, depending upon the application, a damping treatment is considered to be effective if the vibrational reduction caused by the damping treatment in turn results in a decrease in at least one of the following: sound radiation; structural stresses attendant fatigue problems in structural members; and, structural-borne wave propagations (i.e., the transmission of vibrational energy along the structure).